BlackTreeCVE Intelligence
← Back to the CVE catalogue
Full vulnerability report · 2026
CVE-2026-68173High confidence

ublk: wait on ublk_dev_ready() instead of ub->completion

Linux · Linux

7.1HighCVSS 3.1
Recommended action
Patch only the product branches with a verified fix

High technical severity; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 89 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Medium, lowered one band.downgradedsince 17 Aug 2026

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • Exploitation requires an existing local or physical foothold with privileges.
  • EPSS is 0.17% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict local access and enforce least privilege on affected hosts.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Linux Linux and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: As exposure requiresRemediation target: Within 365 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 89 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Distribution package intelligence

Release-specific package status

Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

17 package states
Package result overrides the generic status

BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 13 affected package states shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.

Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourcelinuxNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourcelinuxNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourcelinuxVendor fix publishedDebian records a fixed source-package version for this release.7.1.6-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourcelinuxVendor fix publishedDebian records a fixed source-package version for this release.7.1.6-1Debian Security Tracker ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-aws-6.14Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-azure-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-azure-fde-6.14Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-azure-nvidia-6.14Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-gcp-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-hwe-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-lowlatency-hwe-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-nvidia-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-oem-6.11Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-oracle-6.14Affected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-raspi-realtimeAffected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-realtimeAffected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivelinux-riscvAffected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-68173 · CSAF 2.0 · revision 3 · status not statedRed Hat Product Securitykernel: ublk: wait on ublk_dev_ready() instead of ub->completion
76 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • kernel as a component of Red Hat Enterprise Linux 10
  • kernel-64k as a component of Red Hat Enterprise Linux 10
  • kernel-64k-core as a component of Red Hat Enterprise Linux 10
  • kernel-64k-debug as a component of Red Hat Enterprise Linux 10
  • kernel-64k-debug-core as a component of Red Hat Enterprise Linux 10
  • kernel-64k-debug-devel as a component of Red Hat Enterprise Linux 10
  • kernel-64k-debug-devel-matched as a component of Red Hat Enterprise Linux 10
  • kernel-64k-debug-modules as a component of Red Hat Enterprise Linux 10
  • kernel-64k-debug-modules-core as a component of Red Hat Enterprise Linux 10
  • kernel-64k-debug-modules-extra as a component of Red Hat Enterprise Linux 10
  • kernel-64k-devel as a component of Red Hat Enterprise Linux 10
  • kernel-64k-devel-matched as a component of Red Hat Enterprise Linux 10
Summary
A flaw was found in the `ublk` component of the Linux kernel. This vulnerability occurs when the `ublk` server sends an `END_USER_RECOVERY` command without a successful `START_USER_RECOVERY`. This can cause I/O requests to become stranded, leading to subsequent file system synchronization operations (fsync) to pile up in an uninterruptible sleep state. The most significant consequence is a system hang, effectively resulting in a Denial of Service (DoS).
Remediation
Fix deferred
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-55274

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix

High technical severity; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 89 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

In the Linux kernel, the following vulnerability has been resolved: ublk: wait on ublk_dev_ready() instead of ub->completion ub->completion is only re-armed by a successful START_USER_RECOVERY. If the ublk server sends END_USER_RECOVERY without one - e.g. its START failed with -EBUSY and the error was ignored - the wait is satisfied by the stale completion of the previous recovery cycle, and the device is marked LIVE and the requeue list kicked while the FETCH stream is still running and ubq->canceling is still set. The kick redispatches a previously requeued request, __ublk_queue_rq_common() sees ->canceling and parks it again via __ublk_abort_rq(), and after the last FETCH clears ->canceling nothing ever kicks the requeue list again: the request is stranded there while holding its tag. If it is the flush machinery's flush_rq, every subsequent fsync piles up in uninterruptible sleep and teardown hangs on tag draining. This matches a report of a lost PREFLUSH with ext4 on top of ublk after daemon crash recovery. ub->completion is an edge-triggered latch used as a proxy for the level condition "every queue has fetched all I/O commands", which can regress (F_BATCH's UNPREP, daemon death) and whose re-arm can be skipped. Drop it and wait on the real condition instead: the new helper ublk_wait_dev_ready_and_lock() waits on ublk_dev_ready() via wait_var_event_interruptible(), woken from ublk_mark_io_ready(), then re-checks it under ub->mutex, waiting again on regression, and returns with the mutex held and readiness guaranteed. Readiness becomes true in the same ub->mutex critical section that clears the last queue's ->canceling, so END_USER_RECOVERY marks the device LIVE and kicks the requeue list strictly after ->canceling clears. The wait stays interruptible, so a server whose daemon died can still be signalled out. For ublk_ctrl_start_dev() this replaces the fail-fast -EINVAL on an F_BATCH ready->UNPREP regression with waiting until the device is ready again.

What

In the Linux kernel, the following vulnerability has been resolved: ublk: wait on ublk_dev_ready() instead of ub->completion ub->completion is only re-armed by a successful START_USER_RECOVERY. If the ublk server sends END_USER_RECOVERY without one - e.g. its START failed with -EBUSY and the error was ignored - the wait is satisfied by the stale completion of the previous recovery cycle, and the device is marked LIVE and the requeue list kicked while the FETCH stream is still running and ubq->canceling is still set. The kick redispatches a previously requeued request, __ublk_queue_rq_common() sees ->canceling and parks it again via __ublk_abort_rq(), and after the last FETCH clears ->canceling nothing ever kicks the requeue list again: the request is stranded there while holding its tag. If it is the flush machinery's flush_rq, every subsequent fsync piles up in uninterruptible sleep and teardown hangs on tag draining. This matches a report of a lost PREFLUSH with ext4 on top of ublk after daemon crash recovery. ub->completion is an edge-triggered latch used as a proxy for the level condition "every queue has fetched all I/O commands", which can regress (F_BATCH's UNPREP, daemon death) and whose re-arm can be skipped. Drop it and wait on the real condition instead: the new helper ublk_wait_dev_ready_and_lock() waits on ublk_dev_ready() via wait_var_event_interruptible(), woken from ublk_mark_io_ready(), then re-checks it under ub->mutex, waiting again on regression, and returns with the mutex held and readiness guaranteed. Readiness becomes true in the same ub->mutex critical section that clears the last queue's ->canceling, so END_USER_RECOVERY marks the device LIVE and kicks the requeue list strictly after ->canceling clears. The wait stays interruptible, so a server whose daemon died can still be signalled out. For ublk_ctrl_start_dev() this replaces the fail-fast -EINVAL on an F_BATCH ready->UNPREP regression with waiting until the device is ready again.

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

What

In the Linux kernel, the following vulnerability has been resolved: ublk: wait on ublk_dev_ready() instead of ub->completion ub->completion is only re-armed by a successful START_USER_RECOVERY. If the ublk server sends END_USER_RECOVERY without one - e.g. its START failed with -EBUSY and the error was ignored - the wait is satisfied by the stale completion of the previous recovery cycle, and the device is marked LIVE and the requeue list kicked while the FETCH stream is still running and ubq->canceling is still set. The kick redispatches a previously requeued request, __ublk_queue_rq_common() sees ->canceling and parks it again via __ublk_abort_rq(), and after the last FETCH clears ->canceling nothing ever kicks the requeue list again: the request is stranded there while holding its tag. If it is the flush machinery's flush_rq, every subsequent fsync piles up in uninterruptible sleep and teardown hangs on tag draining. This matches a report of a lost PREFLUSH with ext4 on top of ublk after daemon crash recovery. ub->completion is an edge-triggered latch used as a proxy for the level condition "every queue has fetched all I/O commands", which can regress (F_BATCH's UNPREP, daemon death) and whose re-arm can be skipped. Drop it and wait on the real condition instead: the new helper ublk_wait_dev_ready_and_lock() waits on ublk_dev_ready() via wait_var_event_interruptible(), woken from ublk_mark_io_ready(), then re-checks it under ub->mutex, waiting again on regression, and returns with the mutex held and readiness guaranteed. Readiness becomes true in the same ub->mutex critical section that clears the last queue's ->canceling, so END_USER_RECOVERY marks the device LIVE and kicks the requeue list strictly after ->canceling clears. The wait stays interruptible, so a server whose daemon died can still be signalled out. For ublk_ctrl_start_dev() this replaces the fail-fast -EINVAL on an F_BATCH ready->UNPREP regression with waiting until the device is ready again.

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
local access → vulnerable operation → disrupt the affected service
Attack surface
Local
Privileges required
Low: a basic authenticated account is required
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration.
CWE not yet assigned
CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
Denial of service
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2026-2730Linux Kernel: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen im Linux Kernel ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen, darunter möglicherweise die Ausführung von beliebigem Code, die Ausweitung von Berechtigungen, die Offenlegung von Informationen, die Manipulation von Daten oder Denial-of-Service-Zustände.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260812Security Bulletin 12 Aug 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 12 Aug 2026, published on 12 August 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix availability varies by product
Affected
Fixed
Linux: < 6.15, 6.18.42 ≤ 6.18.*, 7.1.6 ≤ 7.1.*, 7.2 ≤ *
Action
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround
No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04

Evidence and provenance

Published 10 Aug 2026 · Last source change 17 Aug 2026, 05:00 UTC · CWE not yet assigned

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-55274
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceUnavailable
NVD statusNVD received

Missing structured fields: CWE classification. Missing data is not evidence of low risk; review the primary advisory.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b < 7dd26adf7e7d482af524e3a0cca4a81ef7c159d0; 728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b < 8f188dd11a1c2ad94caeaee36ef68bb8221d4a12; 728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b < 432a9b2780c0a01caf547bd1fc2fcf28aeb8d173; 42ea64e01c96e594fb4f80c54dfe4f934d008a6e; 6.14.6 < 6.15; 6.15 · Fixed: < 6.15; 6.18.42 ≤ 6.18.*; 7.1.6 ≤ 7.1.*; 7.2-rc5 ≤ *
    After
    728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b < 7dd26adf7e7d482af524e3a0cca4a81ef7c159d0; 728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b < 8f188dd11a1c2ad94caeaee36ef68bb8221d4a12; 728cbac5fe219d3b8a21a0688a08f2b7f8aeda2b < 432a9b2780c0a01caf547bd1fc2fcf28aeb8d173; 42ea64e01c96e594fb4f80c54dfe4f934d008a6e; 6.14.6 < 6.15; 6.15 · Fixed: < 6.15; 6.18.42 ≤ 6.18.*; 7.1.6 ≤ 7.1.*; 7.2 ≤ *
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-55274↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-68173 · cve.blacktree.nl